1. Field of the Invention
The present invention relates to an image writing unit, an image forming apparatus, an image writing method and a computer-readable information recording medium, and in particular, to an image writing unit and an image writing method for making it possible to reduce possible degradation of image quality which may otherwise occur upon density transformation in an image forming apparatus in which a plurality of light emitting device array units (hereinafter simply referred to as LPHs (LED (Light Emitting Diode) Print Heads)) are arranged in a staggered manner, each of which has a length shorter than a length of a photosensitive body in a main scan direction, the image forming apparatus, and a computer-readable information recording medium storing an image writing program which causes a computer to perform the image writing method.
2. Description of the Related Art
For example, Japanese Laid-Open Patent Application No. 10-65907 discloses an art for reducing possible degradation in image quality which may otherwise occur upon density transformation in an image forming apparatus. According to the art, smoothing processing is carried out on input binary image data, and density increasing transformation is carried out suit that image density is increased predetermined integer times. Next, on binary image data thus having undergone the density increasing transformation, density reducing transformation is carried out such that image density is reduced predetermined integer times. Further, on binary image data thus having undergone the density reducing transformation, processing of reducing a line width is carried out. Image data thus having undergone the processing of reducing a line width is then output.
The above-mentioned art includes an art of a type of size change processing in which image density is increased 1.5 times such that image data of 400 dpi is transformed into image data of 600 dpi, in a so-called “wide machine” for an A0-size. In the size change processing, with the use of software, image density is changed 1.5 times in each of a main scan direction and a sub-scan direction. Because software is used as mentioned above, a considerable time may be required for the size change processing. Reduction of the required time is preferable.
In order to reduce the required time, the size change processing may be carried out with the use of hardware instead of software. Thereby, it may be possible to carry out the size change processing of changing image density 1.5 times in each of the main scan direction and the sub-scan direction approximately in a real-time manner. Thus, it may be possible to output image data having undergone the size change processing rapidly.
As the above-mentioned wide machine, an image forming apparatus which uses an LPH for multi-level exists. In the size change processing in the image forming apparatus, binary 400 dpi image data read from an image information storing unit is transformed into “multi-level” 600 dpi image data. In the image forming apparatus, it is possible to carry out the size change processing with reduced image quality degradation with the use of various 1.5-time density size change algorithms.
However, in such an image forming apparatus which uses an LPH for binary, size change processing may be carried out such that binary 400 dpi image data is transformed into “binary” 600 dpi image data. In this case, it is not possible to use middle-tone image data which is “multi-level” image data because the image forming apparatus uses “binary” image data as mentioned above. Further, when the size change processing is carried out with the use of a matrix pattern, a line width may vary in an image obtained from the size change processing, according to a position in a matrix of the matrix pattern. Therefore, a problem may occur such that image quality should be maintained when the size change processing of changing image density 1.5 times in each of the main scan direction and the sub-scan direction is carried out with the use of hardware at high speed.
Japanese Laid-Open Patent Application No. 2008-100468 discloses a related art.